ISO 13347-4:2004

Overview - ISO 13347-4:2004 (Sound intensity method)

ISO 13347-4:2004 specifies a standardized laboratory method for determining the airborne sound power levels of industrial fans using the sound intensity method. It applies to industrial fans as defined in ISO 5801 and ISO 13349 and is limited to airborne sound emission (vibration effects are excluded). The procedure measures sound intensity on a measurement surface that encloses the fan (or fan inlet/outlet) and provides reproducible results across qualified test facilities.

Key topics and technical requirements

• Measurement principle: Sound power is derived from measured sound intensity over a defined measurement surface surrounding the source. The approach is based on ISO 9614-1 and adapted for fans.
• Test set-ups: Set-ups are designed to reflect the physical orientation expected in installations compliant with ISO 5801; configurations cover free-standing and ducted arrangements.
• Instrumentation & qualification:
  • Use of a calibrated Reference Sound Source (RSS) to qualify instrumentation and personnel and to derive site adjustments.
  • Calibration checks before and after tests using an acoustical calibrator conforming to IEC 61094-2 (typical accuracy ±0.5 dB).
  • Field check by rotating the intensity probe (180°) to verify probe/system consistency; defined tolerances per octave bands.
  • Periodic performance verification against a calibrated RSS with specified tolerance limits across octave bands.
• Acoustical environment controls:
  • Background noise and reverberant sound at the measurement surface must not exceed direct sound from the fan.
  • Nearby reflecting surfaces should be representative of typical installations; excessive reflections or reverberation may invalidate results.
• Data handling:
  • Measurement sets are checked by comparing full and half-data sets to confirm sampling adequacy.
  • Calculations include surface-area weighting and corrections (e.g., duct-end corrections) based on RSS measurements.

Applications - who uses ISO 13347-4

• Fan manufacturers for standardized noise ratings and product specification.
• Independent acoustical test laboratories performing certified fan sound power determinations.
• Acoustic consultants and HVAC engineers estimating installation sound pressure levels and comparing fan options.
• Regulatory and procurement teams requiring reproducible, comparable sound-power data for compliance, selection, or tendering.

Related standards

• ISO 13347-1, -2, -3 (other parts of the fan sound-power series)
• ISO 5801 (fan performance testing / installation orientation)
• ISO 9614-1 / ISO 9614-2 (sound intensity measurement methods)
• ISO 5136 (in-duct methods)
• ISO 13349 (vocabulary)
• IEC 61094-2 (microphone calibration)

Keywords: ISO 13347-4:2004, industrial fans, sound power levels, sound intensity method, acoustic measurement, fan noise testing, RSS calibration, ISO 5801.